Implantable hearing aid systems such as for example middle ear devices, implantable bone conductors and cochlear implants include an implanted receiver device that receives a signal from an external transmitter device via an inductive link. Both sound information and electrical energy are usually transmitted from the external transmitter device to the implanted receiver device via the inductive link. The implanted receiver device includes or is connected to an implant stimulator to stimulate the hearing organ. The implant stimulator may, for example, be a vibrator or an electrode array. For these types of implantable hearing aid systems, the external transmitter device is usually kept in place with a magnetic attachment, so there are magnetic materials in both the external transmitter device and in the implanted receiver device. These two units attract each other to keep the external transmitter device in position and retained on the head of the user.
A drawback of these systems is that the magnetic force presses the external transmitter device towards the skin which may cause skin irritation or even skin necrosis. The external transmitter device may also accidentally slide off from the patient's head quite easily. The efficiency of the inductive link is also quite poor since it is necessary to have a relatively thick skin between the implanted receiver and the external transmitter device to avoid skin necrosis due to the constant pressure against the skin. The magnetic material in the implanted receiver device may also hinder or complicate MRI (Magnetic Resonance Imaging) examinations of the user. In case of MRI examinations, the currently available implantable hearing aids usually require surgical removal of the magnet in the implanted receiver device.
To retain the external transmitter device on the head, it has of course been possible to attach an external transmitter device with tape or glue to the patients head but this has not been acceptable as a clinical solution due to, for example, drawbacks of using glue on the external transmitter device making it difficult to remove. Drawbacks of using tape over the external transmitter device include limited access to the external transmitter device as well as limited aesthetics.
There is a need for more effective implantable hearing aid systems that are reliable and do not have the drawbacks discussed above.